The invention relates generally to an earth-moving device in the form of a tractor-scraper into which soil is propelled by an elevator and which has improved means for scraping the soil and dumping the soil when the scraper bowl is filled.
In many conventional types of scrapers of the elevator type the scraper blade is used both for scraping soil up into the bowl for transport and for leveling or strike-off purposes when the soil is subsequently dumped. Where the scraper blade extends the full width of the bowl and is intended to take a relatively shallow cut the same blade can be used satisfactorily for both scraping and leveling purposes. For example, in some scrapers the scraper blade is secured to the forward edge of a moving floor section. The section is slid rearwardly in the bowl in order to provide a discharge opening, with the blade, during discharge, performing its leveling function.
However, the modern tendency, for more efficient scraping and elevation, is to employ a scraper blade which is much narrower than the width of the bowl and which digs much more deeply, even being provided with projecting ripper teeth to loosen the subsoil. Such blades, when used for strike-off, are, of course, incapable of even or full-width leveling.
In some conventional elevator type scrapers the scraper blade is mounted upon a blade base which is fixed at the front end of the bowl and is an integral part of the bowl structure. In such devices, using a sliding floor section, a separate striker blade is mounted at the front edge of the floor section and serves to level the material which is discharged as the floor section is retracted. This provides the desired full width leveling but any attempt to distribute the discharged soil in a thin layer by lowering of the bowl level has serious clearance problems since the scraper blade, being a fixed part of the bowl, must also be lowered into ground engagement. It is obviously undesirable to be digging furrows in the ground at the same time that one attempts to do finished leveling.
Moreover, wherever the strike-off or leveling function is accomplished by a blade which is secured to the front edge of a slidable floor section, soil cannot be spread to a constant depth. The reason for this is that in retracting the floor section gradually to produce gradual discharge of the contained material, the floor section is guided along a track which is not horizontal but which has a slope depending upon the existing degree of tilt of the bowl, resulting in the spreading of a layer soil of constantly increasing thickness as the movable floor section is gradually retracted.
There are other serious problems in the use of slidable floor sections. The discharge opening is usually only a small fraction of the bottom area of the bowl. While discharge takes place satisfactorily in the case of soils which are relatively dry and friable, obtaining discharge of wet clayey soils is an entirely different matter. The soil in the bowl is, in the usual design of scraper, pressed forwardly toward the discharge opening by an ejector plate. Clay inherently resists ejection and, instead, tends to expand laterally against the side sheets of the bowl and to move forwardly into a jamming position against the flights of the elevator so that instead of smooth discharge there is a condition of "hang-up" which often requires that scraping be discontinued until the earth loses some of its moisture, at considerable loss to the contractor. Moreover, the use of sliding floor sections is accompanied by certain mechanical disadvantages, one being that a floor section is guided on rollers in tracks which are located so low in the structure as to be subject to heavy abuse when pulled over large boulders or abrasive materials. Moreover the tracks, being in exposed position, are susceptible to clogging by clay, rocks and foreign matter and when obstruction of the tracks is unbalanced, as is usually the case, the sliding floor section may become cocked and inoperative.
Similarly the actuators used for operating the movable floor section must be mounted low in the structure in a position to exert pressure in line with the tracks, and such actuators are, therefore, vulnerable to damage by casual ground obstructions. Where such actuators are, instead, mounted behind the ejector plate they create space and accessibility problems, especially where a rear driving engine is employed.